The-present invention relates to video format conversion apparatus and method for a television (TV), and more particularly to video format conversion apparatus and method for a TV for converting an interlaced video format into a progressive video format.
High definition TVs (HDTVs) of the interlaced scanning system developed in Japan are currently used experimentally on the air. These HDTV's can easily use a video source because their peripheral appliances such as cameras and video cassette recorders have already been developed. With progressive scanning HDTV systems developed in the U.S.A., it is difficult to utilize a video source of the progressive scanning system because no peripheral appliances have been developed. In the latter case, therefore, video of the interlaced scanning format must be converted into a video of the progressive scanning format. In particular, the format of videos displayed on a monitor should be of the progressive scanning system. For transmitting compressed videos of the interlaced scanning format, accordingly, it is important and essential to efficiently convert them into the progressive scanning format as a display format.
In conventional analog systems, pixel (line) interpolation for NTSC TV or digital TV is carried out using one oil the following methods:
First, the intra-field interpolation that involves to interpolating lines not scanned using scanned lines in the current field. Although this method is the most simple, there is a problem of a deterioration in resolution because each line is interpolated by the mean value of pixels on scanned upper and lower lines positioned with respect to the line to be interpolated.
Second, the inter-field interpolation that involves simply interpolating lines not scanned using scanned lines of the current field and other fields, without any motion compensation. Although this method recovers videos with high resolution for stationary video portions, there is a problem of a severe artifact for motion-involved video portions.
Third, the interpolation with motion compensation can be used. This method solves the problems encountered in the intra-field interpolation method and the inter-field interpolation method.
In accordance with the interpolation method involving the motion compensation, motion information is searched. Based on the searched motion information, a video scene is divided into a stationary video portion and a motion video portion which will be adaptively interpolated.
For example, the stationary video portion is substituted by the mean value of two successive frames while the motion video portion is subjected to a motion compensation. For a scene change, the intra-field interpolation is adopted so as to maximize the efficiency.
Now, a general method of converting a video of the interlaced scanning format into a video of the progressive scanning format using the interpolation with motion compensation in a digital HDTV will be described.
In this case, reference frames are needed for the motion compensation. In accordance with techniques recently proposed, two frames t-1 and t+1 respectively just preceding and just following the current frame t are used as reference frames. For these reference frames, motion-compensated videos are used in order to achieve an as accurate an interpolation as possible. For the previous frame t-1, in particular, videos already converted into those of the progressive scanning format are used so that they can be time-recursive. For the next frame, lines not scanned are substituted by the mean value of optional upper and lower scanned lines.
In order to seek a motion, motion compensation is carried out using identical motion information by equal sized blocks each including, for example, 16 by 8 pixels in accordance with the block matching algorithm.
In this case, first, the current frame to be interpolated is divided into equal sized blocks each including, for example, 16.times.8 pixels. For the current block to be interpolated, motion information is sought from the previous frame and the next frame.
Since lines in half of each block to be interpolated are those not scanned, lines being used for seeking motion information correspond to those in the remaining half scanned.
Using the motion information sought as mentioned above, lines not scanned are interpolated. As useful methods for such an interpolation, there are: a method utilizing a compensation based on the previous frame, a method utilizing a compensation based on the next frame, and a method utilizing a substitution by the mean value of signals compensated from the previous frame and the next frame. Among these methods, one yielding the minimum error is selectively used.